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Re: [PATCH], Add optional IEEE/IBM long double multilib support
- From: Joseph Myers <joseph at codesourcery dot com>
- To: Jakub Jelinek <jakub at redhat dot com>
- Cc: Michael Meissner <meissner at linux dot vnet dot ibm dot com>, GCC Patches <gcc-patches at gcc dot gnu dot org>, Segher Boessenkool <segher at kernel dot crashing dot org>, David Edelsohn <dje dot gcc at gmail dot com>, Bill Schmidt <wschmidt at linux dot vnet dot ibm dot com>
- Date: Fri, 5 Jan 2018 17:47:39 +0000
- Subject: Re: [PATCH], Add optional IEEE/IBM long double multilib support
- Authentication-results: sourceware.org; auth=none
- References: <20180104230555.GA4847@ibm-tiger.the-meissners.org> <20180105173350.GD1833@tucnak>
On Fri, 5 Jan 2018, Jakub Jelinek wrote:
> On Thu, Jan 04, 2018 at 06:05:55PM -0500, Michael Meissner wrote:
> > This patch is the beginning step to switching the PowerPC long double support
> > from IBM extended double to IEEE 128-bit floating point on PowerPC servers. It
> > will be necessary to have this patch or a similar patch to allow the GLIBC team
> > to begin their modifications in GLIBC 2.28, so that by the time GCC 9 comes
> > out, we can decide to switch the default. It is likely, the default will only
> > be switched on the 64-bit little endian PowerPC systems, when a distribution
> > goes through a major level, such that they can contemplate major changes.
>
> When you're mentioning multilibs, does that mean that we'll have two ABI
> incompatible libgcc.so.* libraries, two ABI incompatible libstdc++.so.*
> libraries etc.? Just one or 2 libc.so.*/libm.so.*?
The existing GCC code tries to fix the libgcc function names so *tf*
always means IBM long double and *kf* always means IEEE long double. As
noted in my reply to this patch, I suspect it might fail to handle
__div?c3, __mul?c3 and __powi?c2 (at least) properly to avoid two
different libgcc ABIs there.
I don't know the intent for libstdc++, libgfortran etc. - but it's been
stated the intent is a single set of glibc libraries. (Of course a
distribution probably has other libraries influenced by the long double
format in some way.)
--
Joseph S. Myers
joseph@codesourcery.com